1. Field of the Invention
The present invention relates to improved metal corrosion inhibited organic acid compositions and methods of using the compositions.
2. Description of the Prior Art
Subterranean hydrocarbon containing formations penetrated by well bores are often treated with aqueous acid compositions to stimulate the production of hydrocarbons therefrom. One such treatment known as "acidizing" involves the introduction of an aqueous acid composition into a subterranean formation under pressure so that the acid composition flows through the pore spaces of the formation. The acid composition reacts with acid soluble materials contained in the formation thereby increasing the size of the pore spaces and the permeability of the formation. Another production stimulation treatment known as "fracture-acidizing" involves the formation of one or more fractures in the formation and the introduction of an aqueous acid composition into the fractures to etch the fracture faces whereby flow channels are formed when the fractures close. The aqueous acid composition also enlarges the pore spaces in the fracture faces and in the formation.
While acidizing and fracture-acidizing well stimulation treatments have been performed successfully over the years, a continuous problem which accompanies the treatments is the corrosion of metal pumps, tubular goods and other equipment used to introduce the aqueous acid compositions into the subterranean formation to be treated. The expense associated with repairing or replacing corrosion damaged tubular goods and equipment can be very high. The corrosion rate of metal equipment and tubular goods is increased by elevated temperatures encountered in deep formations, and the corrosion results in at least the partial neutralization of the aqueous acid compositions before they react with acid-soluble materials in the formations.
Aqueous acid compositions are also utilized in a variety of other industrial applications to contact and react with acid soluble materials. In such applications, metal equipment and metal surfaces are necessarily also contacted with the acid compositions, and the resulting corrosion of such metal equipment and surfaces is highly undesirable.
A variety of metal corrosion inhibited aqueous organic acid compositions for carrying out acidizing and fracture-acidizing stimulation treatments in wells and for performing other acidizing operations have been developed heretofore. For example, the rosin amine derivatives described in U.S. Pat. No. 2,758,970 issued to Sankaitis et al. on Aug. 14, 1956 have been extensively utilized along with other metal corrosion inhibitor components in aqueous organic acid compositions. Such metal corrosion inhibitor formulations have commonly also included large concentrations of thiourea and/or thiourea derivatives which function to intensify the metal corrosion protection afforded by the formulations. However, a disadvantage of the corrosion inhibitor formulations and the aqueous organic acid compositions containing the formulations is that thiourea and its derivatives are highly toxic, i.e., they are considered to be carcinogens and cause damage to living tissue when ingested, inhaled, or absorbed on the skin.
Thus, there is a need for improved metal corrosion inhibited aqueous organic acid compositions which are of low toxicity but still function effectively to minimize metal corrosion.